This invention relates to polymer concrete compositions for use in making corrosion resistant structures and other structural composite elements, as well as methods of making same. Polymer concrete is a term that applies to a variety of composites of polymer and concrete or aggregate, for example. Such composites can be made by impregnating hardened portland cement with a liquid monomeric material that is subsequently polymerized in situ. Alternatively, they can be made by combining monomeric, oligomeric, and/or polymeric material with a fresh Portland cement concrete mixture, which is then subsequently hardened. Other composites referred to as polymer concrete do not contain cement, per se; rather, they are composites made by polymerizing a monomeric, oligomeric and/or polymeric material with filler material, such as aggregate (e.g., gravel, sand, etc.).
Polymer concrete composites have generally good durability and resistance to salts, acids, and other corrosive materials, depending on the formulation. They are, therefore, suitable for use in pipe, tunnel support liners, bridge deckings, sumps, manholes, interceptor structures, and corrosion resistant electrolytic containers, for example. These represent a significant market for use of polymer concrete composites.
The main objective of pipe manufacturers in the early 1960's was to develop a polymer concrete pipe with resistance to corrosion from both acidic and caustic effluents inside the pipe, and from chemical attack outside the pipe. Other objectives included designing significant axial and compressive strengths without adding steel or fiberglass reinforcement. These pipes were mainly used for collection systems in chemical plants with highly corrosive environments. Manufacturing of polymer concrete pipe was slowed down in the late 1960's due to poor mix designs and manufacturing problems, which kept polymer concrete from being an economically viable product.
Traditionally, water or wastewater infrastructures have been constructed of steel reinforced Portland cement concrete, clay tile, brick, and ductile iron, all of which are subject to corrosion or maintenance problems. Anaerobic bacteria cause microbiologically induced corrosion as a result of the formation of waterline condensates of carbon dioxide and hydrogen sulfide gases, which produce sulfuric acid that chemically attacks Portland cement concrete and carbon steel reinforcement. Also, concrete pipe deteriorates rapidly in sewage due to hydrogen sulfide attack, which often erodes the upper surface of the pipe (i.e., that which is open to air), eventually causing a cave-in. An additional detrimental activity is that many concrete pipe systems are purged with caustic and hypochlorite in order to suppress the sulfide odor caused by the sewage.
One way in which Portland cement concrete has been protected from corrosive solutions and environments is to use a protective liner. However, such liners easily tear, leak, or pull away from the concrete. As a result, corrosive solutions, mist, and/or vapor from the wastewater can penetrate the area between the liner and the concrete structure, thereby causing corrosion and failure of the structure. Protective surface coatings are also widely used to protect Portland cement concrete and ductile iron products in wastewater applications. Problems associated with these coatings are similar to the problems associated with plastic liners, as well as problems associated with adhesion, consistent coating thickness, brittleness, installation, and surface preparation.
Another effort to provide a structure which can withstand the highly corrosive environment of the wastewater solution is through the use of polymer concrete. Typical polymer concrete composites are made from one or more thermosetting resins, a promoter, and catalyst to cure the material, along with aggregate. The most commonly used thermosetting resin is an unsaturated polyester resin. The resin within the mix bonds the aggregate, much like Portland Cement does in traditional concrete structures. Polymer concrete can also include fillers such as sand, silica flour, mica flakes, glass spheres, and fiberglass in various sizes.
Although conventional polymer concrete composite structures are a great improvement, many compositions still have numerous disadvantages. Some of the disadvantages include the high cost of fabrication due to the material costs and manufacturing techniques used. There can also be problems with the formation of cold joints from the casting process, which can cause leaking and leaching paths. Polymer concrete structures can also have irregular interior surfaces, which can cause difficulty in cleaning the structure. If external connections are attached to the polymer concrete structures, these can also be the source of leaks and leaching.
A significantly improved polymer concrete composition is known that includes a blend of thermoset and thermoplastic resins. Using a major amount of a vinyl ester resin in the resin blend allows for such compositions to be used in structures exposed to extremely corrosive environments, such as electrolytic containers. Although wastewater structures can be exposed to corrosive conditions, such conditions are not as corrosive as those used in electrolytic mineral processing. Thus, less corrosion resistent compositions could be used. Thus, there is a need for materials that can be used in water and wastewater infrastructures that are sufficiently corrosion resistent yet not as expensive as those used in electrolytic containers.